i get 110 degrees for the heatbed after 4:30 minutes heating and with 4mm glas - after the heating the HRP-300-15 is on 45 degrees and the Power-Expander is on 55 degrees.
i also heating the extruder heater with the heatbed together. no problem for the HRP-300-15
the power expander go after heating on print to 45 degrees and the HRP-300 to 40 degrees
it realy works exellent - maybe the HRP-300-15 have much more reserves
i have print jobs more then 20 hours with 110 degrees heatbed and both extruders and never problems !!
and i have more than one K8400
since 2 weeks i install the power-expander in airstream from the buttom fan - before he go up over 100 degrees but he works good

here is one more picture from my other K8400 - here you see the power-expander in airstream - on the other pictures he is in the black box

i have try much more power supplies - stronger and i also try two power supplies … but nothing works so good like the HRP-300-15 (Reichelt 80 euro)

I’m sure that could work just excellent in your case and your configured setup!
And the major benefit imho is that it’s just swap-able because it has the exact form factor.

But nuance your advice a bit. Besides have u tried heat up all 3 heaters at full blast from cold to hot? Or you first heat the bed, and then heat up the nozzles? Because imho that’s just going to fail and reset your machine… The 300(330) watts just isn’t enough to power it safely.
You just don’t know what other things they have connected, or what situation they have going on.
Besides the HRP-300-15 is actually a 330watts psu (Thats just weird but it’s just the fact… look at the data sheets)
But I want to add just a tiny detail on the 330 watts psu and that’s the following: a psu has a derating curve linked to the environment temperature its working in.

In my specific case the printer is in a sound(heat) insulated box. And when I’m printing big ABS objects its gets insanely hot inside…
My thermometer LCD turns complete black at around 53°C which happened more than once…
But by going of on the second nozzle data and correlating this a bit I think its safe to say it won’t go any much higher than around 60°C

So if I would use the 330watt one it would only be able to deliver about 74% lets say 75% give or take…
(330 / 100) * 75 = 247.5
So in that case the 330 watt can only provide 247.5watts of juice, which is just to little to safely run the thing.

The rsp 500 has exactly the same curve, at 50 starts degrading with a limit at 70.
But the math gives us
(500 / 100) * 75 = 375
375watt is the maximum output which is good enough with some spare watts for a good nice rest

[quote=“Jansinger”]You don´t need 500W ! - all you need is WM (MeanWell) HRP-300-15 an the Rep-Rap Power-Expander !!!
[…]
I don´t know why but it works exellent !
[/quote]
Just to be clear, you’re arguing that we should disregard ratings because you don’t know why something appears to be working?

The HRP-300-15 is rated for 330 W. It has build-in overload protection at 105-135% of rated power, i.e. 347-446 W.

The custom Mk. 3 heat-bed will consume 346 W at full power (15^2/0.65).

According to a message on this forum from Velleman (http://forum.velleman.eu/viewtopic.php?f=64&t=13576#p60375), the printer can draw up to 7 A (peak), at 15 V that would be 105 W. Your max draw would be 346+105 = 451 W. That’s the figure to use unless you like living over the edge. It’s also beyond the 330 W +30% (on a good day) rating.

Either you’re very lucky with your PSU or you’ve limited your system in other ways; e.g. thin cables and/or connector, increased Rdson in power expander MOSFET and/or trace resistance (heat would be the symptom of these), PSU current limiting, et.c. This would lower the heat-beds power consumption.

What is the voltage between the plus and minus solder pads on your heat-bed when heating?

II can’t resize the picture to look closer but the cables to his heatbed seem rather small to me… Looks like 0,75mm or something in that range… I’ve used 2.5 (that’s a total bitch to work with) and those still get pretty hot when heating from cold state…

[quote=“jeafke”]II can’t resize the picture to look closer but the cables to his heatbed seem rather small to me… Looks like 0,75mm or something in that range… I’ve used 2.5 (that’s a total bitch to work with) and those still get pretty hot when heating from cold state…

[quote=“danf”][quote=“Jansinger”]You don´t need 500W ! - all you need is WM (MeanWell) HRP-300-15 an the Rep-Rap Power-Expander !!!
[…]
I don´t know why but it works exellent !
[/quote]
Just to be clear, you’re arguing that we should disregard ratings because you don’t know why something appears to be working?

The HRP-300-15 is rated for 330 W. It has build-in overload protection at 105-135% of rated power, i.e. 347-446 W.

The custom Mk. 3 heat-bed will consume 346 W at full power (15^2/0.65).

According to a message on this forum from Velleman (http://forum.velleman.eu/viewtopic.php?f=64&t=13576#p60375), the printer can draw up to 7 A (peak), at 15 V that would be 105 W. Your max draw would be 346+105 = 451 W. That’s the figure to use unless you like living over the edge. It’s also beyond the 330 W +30% (on a good day) rating.

Either you’re very lucky with your PSU or you’ve limited your system in other ways; e.g. thin cables and/or connector, increased Rdson in power expander MOSFET and/or trace resistance (heat would be the symptom of these), PSU current limiting, et.c. This would lower the heat-beds power consumption.

What is the voltage between the plus and minus solder pads on your heat-bed when heating?[/quote]

…and don´t forget - i use 2x66W heater and not the 2x30W original
maybe the reprap power-expander throttles it. but i am in 4:45 on 110 degrees
…and i use the same configuration on 2 printer !
i heat both extruder and the heatbed together - without problems
if it were close to the limit i think i could not do long time printjobs (20hours) without problems
I have no crashes and no irregularities in my Print - my prints have a exellent qualität
…and I use other belt which are highly tensioned. for this I had the step motors bring to their limit (0,925V)
these are all things that a power supply actually not love

i would like to know what the heatbed really consumed - but my multimeter only go up to 10A

[quote=“Jansinger”][quote=“jeafke”]II can’t resize the picture to look closer but the cables to his heatbed seem rather small to me… Looks like 0,75mm or something in that range… I’ve used 2.5 (that’s a total bitch to work with) and those still get pretty hot when heating from cold state…

Kind regards
JeAfKe[/quote]

i use 2,5²[/quote]

Really on that case I’m sorry? Apologies for my ignorance.

But you got to admit this looks beefier (I guess its the insulator that has a different thickness.)

So you can run everything on a 330 psu that’s nice to know that’s a possibility which goes against any common sense.
But advising to ignore common sense and hope it works with every setup isn’t what I want to do.

You should assume continous 23 A at 15 V for the heat-bed. You’re using the reprap power expander, rated for max 20 A continuous connected to screw terminals likely not rated for more than 10-12 A. Heat-bed power goes through a molex style connector, likely rated for 10-12 A. Even at those lower currents, the pins will heat up.

Now, this still works for you, likely because of the fact that 492 W is a peak figure. The heat-bed only consumes 346 W at start, then its PCB traces heat up and increases the 0.65 ohm resistance. I measured 18 A (270 W) at 100 degrees C when ON. It works because you’re only intermittently over 135% of 330 W.

Still, going by ratings, you have negative headroom in multiple areas (including PSU). If that’s something you want to recommend and argue for, at least try to understand 1) why it works, 2) the risks involved.

4 minutes and 45 seconds is however not a very bad figure. I get to 110 degrees C (thermistor location) in 4 minutes 36 seconds. That’s using non-insulated head-bed with 3 mm window glass covered in a kapton sheet.

Have a question regarding Jansingers setup. Im guesing your using the 12V setup on the bed. Im wondering if your using one of the heating circuits or both. I know there are those that have chosen just to use one of the circuits making it heating one side of the bed faster then the other but eventually it even out the heat on the aluminium. Atleast that is the theory. Could it be the reason why you have the ability like your setup give?

[quote=“Marlark”]Have a question regarding Jansingers setup. Im guesing your using the 12V setup on the bed. Im wondering if your using one of the heating circuits or both. I know there are those that have chosen just to use one of the circuits making it heating one side of the bed faster then the other but eventually it even out the heat on the aluminium. Atleast that is the theory. Could it be the reason why you have the ability like your setup give?

Best regards
Marlark[/quote]

if you only use one 12V circuits on the bed you never get 110 degrees - only 100 in the middle - it´s the (near) same if you use the 24V pin with only 15V
i have a big permanent bridge between pin 2+3

True I know of two that have experimented with one circuit. For the most they only needed getting 60 or 90 degrees. Myself i use 24V PSU on the 24V circuit so can’t say I have had much reason to experiment with it. But my gut feeling is doing it that way would mean heat dif dissipation over the plate.

Can somebody please help me? In a few months I burned my second Power Expander and want to turn over to a SSR. But all those explanations on this forum from technicians are great, but for someone not knowing anything about electronics its hard to get.
It’s about a 15V PSU and Marlark’s heatbed (12V option). I made the connections like this, but it doesn’t work. The SSR-led burns red, the display shows the temp 19/0, but the heatbed is not warming up. Is there a wrong connection?

I don’t know for sure if thats going to work @svdv the input terminal 4 and 3 should be good, but the switching terminals 1 and 2 say VAC (alternating current) anyway try hooking it up, connect 1 terminal to the + of the PSU and the 2 terminal to the heatbed, and a straight from the - side of the PSU to the - on the heatbed I would guess… But if that doesn’t work I assume it really only is capable of switching AC loads… But that does make sense cuz it says 24 ~ 380VAC Oh yeah, u got it hooked to a 15V PSU… I guess those numbers 24 ~ 380 VAC really mean something But 24V AC is actually a 48V difference between the peaks in the sinus, so I would think it could (maybe) work with a 48V DC load??? Or thats just bullocks? <= I really want someone to explain the whole solidstate relais thing in depth if possible… I have absolutely no experience in using such a thing…

I’m using a powerexpander based on raby’s design, I burned one mosfet when I tried to heat the bed without any heatsink sticking to the mosfet, but afterwards I superglued a piece a scrap aluminum against it and its running for a long while now without issues…

As a consequence, you cannot use it. The input is not a problem, it should work in your configuration. However, there Must be (!) an AC supply for the power side, since it is a pure thyristor switch implemented (like in the dimmer for home lights). These parts need a high trigger voltage, so you can hardly operate this below 24V AC. Normally, these circuits are protected against undervoltage, so they won’t react at voltage below 24V. Sorry for that.

Thanks for your respons. In several posts this SSR was mentioned. But maybe with use of a 24V PSU. Like I said, with regards to electronics I can only copy from what others say…
But do you think there’s a SSR I can use in this case?

I checked the web for suitable SSD relays, a possible candidate would be the D1D12 from crydom. To get you some key parameters for alternative devices:

input voltage: must be larger than 15V. This is the voltage the controller is providing. However, you may need to install a parallel resistor to the input connections to ensure a proper switching off of the output stage.

The output current shall be at least 12 A (180W at 15V), at least as high as the nominal output current of your PSU. The next stronger part from crydom is for 40A (D1D40)
At installation you have to take care on the polarity!

I haven’t seen comparable parts from FOTEK, this crydom part is available at Mouser for approx. 55 Euro. I have seen power adaptor boards in the 3D printer community for much less money, So it is worth to check these parts, although they dont look so much “professional”.

Hi hoh61
You’re very kind to take all this effort, I really appreciate.
I got a MeanWell RSP 320-15 with a rated current of 20A. So I think I should go for the Crydom D1D40 which costs € 75,–.
The RepRap Power Expander is about € 17,50

On several posts now it is said that a replacement PSU must be at least 500W, so after burning my second Power Expander I decided to use the RSP-320-15 only for the heatbed and put the original PSU RS-150-15 back in the printer.

I can imagine two options:

To purchase a 24V PSU (only for the heatbed, about 350W) with the use of the Fotek SSR. That should do, I think?

Try again a RepRap Power Expander (and still use this PSU only for the heatbed), although I don’t know what I am doing wrong to burn it after a while. First time I used too thin wires, but second time I replaced them for thicker wires.

Is there another sensible or even more sensible solution which can be done by an electronics-dummie? The sour thing is that mostly I use PLA and PETG without heatbed and only occasionally I print ABS with the heated bed.

edit: I just saw that Hsoubry in this post earlier used a 4 euro SSR DC-DC 25A 3-32VDC/5-60VDC W6…

I see a lot is going on about using a SSR to switch the headed bed.
An SSR like the Fotek SSR-40DA will NOT work. It is expecting an alternating current (AC). Even if it will switch ON, it will likely not switch off and result in overheating. So do not use an SSR labeled DA or AA. Only a DD (dc in, dc out) SSR could work.

I have tried the SSR DC-DC 25A 3-32VDC/5-60VDC because it was cheap. It should work for 5 to 60 V dc and up to 25A. But with the 15V PSU the headed bed nearly draws 23A, so very little margin. Knowing the SSR is cheap Chinese crap, that also didn’t work very well. The SSR was heating up faster than the heated bed
So, don’t use these cheap SSR DC-DC 25A 3-32VDC/5-60VDC . It does not work !

Will the cheap 40A version work ? Maybe, but i did not like to try it any more.

So now I work with the a Mos-FET (IRF1324PbF) solution as in a post from danf on feb 20.